Safety device in motor winch

ABSTRACT

A safety device includes a resistance, a condenser and a relay winding which are star-connected across a three-phase source of AC potential providing the supply potential for a three-phase motor which is controlled, as to operation in the normal and reverse directions, by a three-phase magnetic contactor connected to the motor by forward or normal and reverse end limit switches. The safety device further includes a normally closed contact which is opened upon energization of the relay winding, and this contact is connected in series in the control circuit of the electromagnetic contactor. This control circuit is connected to the same single phase as is the series connection of the condenser and the relay winding. If the three-phase source of AC potential does not have the proper phase sequence, or if a single phase is inoperative, the relay winding is sufficiently energized to open the normally closed contact and thus interrupt energization of the magnetic contactor with resultant deenergization of the three-phase motor driving the winch.

United States Patent 1191 Ishikawa 1 1 3,708,719 1451 Jan. 2, 1973 [54]SAFETY DEVICE 1N MOTOR WINCH [75] Inventor: Shogo Is'hikawa, Kawasaki,Japan [73] Assignee: Kabushiki Kaisha Kito,-Kanagawaken,Japan [22]Filed: June 21,197]

21 Appl.No.: 154,836

[30] Foreign Application Priority Data Primary Examiner-James D.Trammell Attorney-John J. McGlew et al.

57 ABSTRACT A safety device includes a resistance, a condenser and arelay winding which are star-co'nnectedacross a three-phase source of ACpotential providing the supply potential for a three-phase motor whichis controlled, as to operation in the normal and reverse directions, bya three-phase magnetic contactor connected to the motor by forward ornormal and reverse end limit switches. The safety device furtherincludes a normally closed contact which is opened upon energization ofthe relay winding, and this contact is connected in series in thecontrol circuit of the electromagnetic contactor. This control circuitis connected to the same single phase as is the series connection of thecondenser and the relay winding. If the three-phase source of ACpotential does not have the 3 Claims 5 Drawing Figures PATENTED JM 2I973 FIG.

RST

FIG. 3

INVENTOR.

SHOGO \samnun BY 2 5 I amma SAFETY DEVICE IN MOTOR WINCH FIELD OF THEINVENTION This invention relates to three-phase motors, particularly tosuch motors driving portable winches, and more particularly to a novel,improved and simplified safety device for preventing operation of athree-phase AC winch motor responsive to improper phase sequence of athree-phase AC source of potential or a failure of one or more phases ofthe source.

SUMMARY OF THE INVENTION This invention is directedto a safety devicefor connecting a winch, driven by a three-phase AC motor to athree-phase AC source of potential, and operable to protect the winchand to secure safety of winch operation by preventing operation of thewinch in case of an improper phase sequence or phase reversal of thethree-phase AC source of potential or in thecase of failure of one ormore of the phases of the source. To this end, the safety devicecomprises a resistor, a condenser and an electromagnetic relay windingstar-connected to the three-phase source of AC potential, with the relaywinding controlling a normally closed relay contact connected in seriesin a control circuit for an electromagnetic contactor, of themotor-reversing type, connecting the winch motor to the three-phase ACsource in series with normal and reverse end limit switches. a

The control circuit of the electromagnetic contactor is connected acrossa single phase of the AC source, and the series connection of thecondenser and the relay winding is also connected across the same singlephase of the source. By virtue of these connections, the safety deviceassures safety of operation of the motor winch by making impossibleoperation of the winch in case of phase reversal or phase failure of thethreephase AC source, with the relay winding being sufficientlyenergized, in case of such phase reversal or phase failure, to open therelay contact in the control circuit resulting in de-energization of theelectromagnetic contactor and corresponding de-energization of the winchmotor, or resulting in inability to close the magnetic contactor foroperation of the motor in either direction.

For an understanding of the invention, reference is made to thefollowingdescription of a typical embodiment thereof as illustrated inthe accompanying draw- BRIEF DESCRIPTION OF THE DRAWING In the Drawing:

FIG. 1 is a schematic wiring diagram illustrating the safety device ofthe present invention connected in the energization and control circuitof a winch driven from a three-phase AC source of potential byathree-phase AC motor controlled by a reversing type magnetic contactorconnected to the motor in series with normal and reverse end limitswitches;

FIG. 2a is a vector diagram of the three-phase voltage of the source;

FIG. 2b is a diagram illustrating the correct phase connections and thecorresponding vector diagram with a proper phase sequence;

FIG. 2c is a diagram, similar to FIG. 2b, showing the conditions with aphase reversal; and

FIG. is a vector diagram illustrating the conditions upon failure of aphase of the three-phase source of potential, or the open phasecondition.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, athree-phase source of AC potential is represented by the threeconductors R, S and T. A magnetic contactor including a normal orforward set of contacts M1 and a reverse set of contacts M2 is connectedbetween the conductors R, S and T and a three-phase AC motor M driving awinch, end limit switches Ls being connected in series between eachsection of the magnetic contactor and motor M. A control circuit for themagnetic contactor is connected, through the medium of a transformer,across the phase S-T of the three-phase source, and includes a normal orforward normally open manually operable push button MI and a reversenormally open manually operable push button M2. Push button M1 isconnected, in series with a normally closed contact M2 of the reversesection M2 of the magnetic contactor to an operatingwinding M1 forclosing the normally open contacts of the forward section MI of themagnetic contactor. Push button M2 is connected in series with thenormally closed contact MI of the forward section M1 of the magneticcontactor in serieswith the operating winding M2 for closing thenormally open contacts of the reverse section M2 of the magneticcontactor. It will be noted that the operating windings M1 and M2 areconnected in parallel with each other but in series in the controlcircuit, with each operating winding being connected in series with itsassociated manually operated push button and the associated normallyclosed interlocking contact of the other section of the magneticcontact.

In accordance with the invention, a safety device NRR is connected tothe three-phase AC source and controls operation of a normally closedrelay contact Lx connected in series in the control circuit, so thatwhen contact Lx is open, it is not possible to energize the magneticcontactor Ml-M2 for motor operation in either direction. The safetydevice includes a resistance Rx, a relay winding Lx and a condenser Cxwhich are star-connected to eachother and to the three-phase conductorsR, S and T. It will be noted that the series connection of relay windingLx and condenser Cx is connected across the phase ST, which is the samephase having the control circuit connected thereacross. When relaywinding Lx is sufficientlyenergized, as described hereinafter, it openscontact Lx to open the series control circuit connected to phase ST.

Referring to FIG. 2a, the vector diagram illustrates voltage vectors V1,V2 and V3, the voltage vector V1 being the potential between conductorsR and S, the voltage vector V2 being the potential between conductor Sand conductor T and the voltage vector V3 being the potential betweenconductor T and conductor R.

With this phase sequence, the connections of the safety device are asindicated at the left in FIG. 2b, with the voltage across the resistorbeing indicated at Rv, that across the relay winding being indicated atLv and that across the condenser being indicated at Cv. The resultantsof these three voltages are indicated in the vector diagram at the rightof FIG. 2b, and it will be noted that the voltage Lv has a relativelysmall magnitude.

On the other hand, and as shown in FIG. 20, when there is a phasereversal as indicated at the left in FIG. 20, the resultant vectordiagram is as indicated at the right in FIG. 20. As indicated at theleft of FIG. 2c, with the phase reversal, resistance Rx is connected toconductor 8 rather than to conductor R, and the relay winding Lx isconnected to conductor R rather than to conductor S. In this case, thevoltage Lv across the relay winding has a much larger magnitude and onewhich is sufficient to effect opening of contact Lx, thus breaking thecontrol circuit for the magnetic contactor and preventing operation ofthe magnetic contactor.

The case with a phase reversal, resulting in there being, in effect,only a single-phase supply, is illustrated in FIG. 3. FIG. 3 illustratesthe condition in which the R phase is open and again it will be notedthat the voltage Rv across the relay winding Lx has a relatively largemagnitude sufficient to effect opening of the contact Lx in series inthe control circuit.

In the event the S phase is open, the voltage between conductors S and Tnaturally decreases to substantially 0. The potential between conductorsS and T is that used for the control circuit, so that theelectromagnetic contactor Ml-M2 cannot be operated as there is novoltage available at the control circuit when the S phase is open. Thesame holds true in case the T phase is open. Thus, the safety devicemakes impossible operation of the winch except in the case where threephase AC power is supplied with a proper phase sequence in which allphases are operative, with operation of the winch being impossible witha phase reversal or the failure of one or more phases. From FIG. 3, itwill be noted that the voltage Lv as opposed to the voltage V2 betweenconductors S and T is impressed on relay winding Lx so that contact Lxis open to open the control circuit.

As a practical example, with a potential difference between conductors Rand S of 220V, the resistor is a resistor Rv (V) of kilo-ohms and 15W,the relay winding is a winding Lv (V) of 200V, the condenser is acondenser Cv (V) of lmF and 600V and the relay operating voltage is150V. The voltages at each component of the relay are then as indicatedin the following table:

Rv(Vl (v(V) I.V(V)

so HZ (10 H7. 50 H1. s0 H1. so H1 60 H1.

Positive phase I 175 m0 155 6| (.5 Negative phase 4X 35 145 245 W0 IltlOpen-phase of R phase 0 0 280 290 I70 215 Open-phase ofS phase )8 I15 II80 0 0 Open-phase of T phase 135 I30 0 0 )6 While a specific embodimentof the invention has been shown and described in detail to illustratethe application of the principles of the invention, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

What is claimed is l. A safety device, for a three-phase motor operatinga winch and connected to a three-phase source of AC. potential through amotor reversing magnetic contactor in series with forward and reverseend limit switches, the magnetic contactor having forward and reverseoperating windin s in a series control circuit energized from a single pase of such source of AC.

claimed in claim 1, including first, second and third conductorsconnected to respective terminals of said three-phase source; saidresistance, condenser and relay winding having first ends connected toeach other; the second ends of said condenser, said relay winding andsaid resistance being connected to said first, second and thirdconductors, respectively; said control circuit being connected to saidfirst and second conductors.

3. A safety device for a three-phase AC motor, as claimed in claim 1, inwhich said operating windings are connected in parallel with each otherin said series control circuit, and each in series witha respectivemanually operable normally open push button.

1. A safety device, for a three-phase motor operating a winch and connected to a three-phase source of A.C. potential through a motor reversing magnetic contactor in series with forward and reverse end limit switches, the magnetic contactor having forward and reverse operating windiNgs in a series control circuit energized from a single phase of such source of A.C. potential, said safety device comprising, in combination, a resistance, a condenser and a relay winding star-connected to each other and to said source with said relay winding being connected across said single phase; and a normally closed relay contact controlled by said relay winding and connected in said control circuit in series with said operating windings; said relay winding being energized to open said normally closed relay contact responsive to a phase reversal of said source or failure of a phase of said source.
 2. A safety device for a three-phase AC motor, as claimed in claim 1, including first, second and third conductors connected to respective terminals of said three-phase source; said resistance, condenser and relay winding having first ends connected to each other; the second ends of said condenser, said relay winding and said resistance being connected to said first, second and third conductors, respectively; said control circuit being connected to said first and second conductors.
 3. A safety device for a three-phase AC motor, as claimed in claim 1, in which said operating windings are connected in parallel with each other in said series control circuit, and each in series with a respective manually operable normally open push button. 